The present invention relates to a fiber optic strain sensor.
Resistive type strain sensors or gages are generally low in sensitivity and stability, possess low gage factors, and are susceptible to electromagnetic interference.
Until recently, the primary objective in fiber optic utilization was transmission of signals requiring a wide band media such as offered by the fiber optics. However, it is also important to consider cases in which the parameter to be measured causes a change in the transmission properties of the fiber itself. In such cases the fiber takes an active part in the detection process. Tab designs handling various fiber sizes were investigated.
Also investigated were both static and dynamic responses comparing fiber optics with resistive strain sensors. Attention was focused on the dynamic comparison of the responses through the utilization of computer programs for presentation and analysis of data. Computer response analysis is essential for quickly evaluating comparison tests for correlation data. Because of their increased sensitivity, due to the less than one square inch size of the fiber optic transducer, and responsiveness due to the areal changes of the fiber optic sensor, the strain tracking capability of fiber optic sensors is excellent.
A comparison of typical systems indicates that a strain induced intensity modulation system is optically simpler, since no interferometry is necessary. However, in both cases, detection finally results from photodetection of optical intensity signals.
The principal object of the invention is to provide a strain sensor which is immune to electromagnetic interference.
An object of the invention is to provide a strain sensor having high gage factors relative to resistive type strain sensors.
Another object of the invention is to provide a strain sensor of great sensitivity, considerably more sensitive than resistive type strain sensors.
Still another object of the invention is to provide a strain sensor of great stability, more stable than resistive type strain sensors.
Yet another object of the invention is to provide a method of manufacture of a pair of tabs for the fiber optic strain sensor if the invention, which method provides ease of handling, mounting, use and fabrication.
An object of the invention is to provide a method of manufacture of a pair of tabs for the fiber optic strain sensor of the invention, which method mechanically develops and maintains the required tolerances for the transconductance quiescent point.
The strain sensors of the invention possess high gage factors/sensitivity, stability and immunity to electromagnetic interference. With high gage sensitivity, the sensors can sense smaller strains and offer better performance capability than resistive type gages. In addition, the sensors of the invention tend to be more stable since their operating or quiescent point is not dependent upon a null or zero crossing effect. Since the sensors are immune to electromagnetic interference, less signal conditioning is required for signal extraction.